1. Field of the Invention
This invention relates to splice detection systems, and more particularly relates to a splice detection system in which a magnetic marker is used to locate a splice between two sections of material. The invention is particularly useful for continuous web manufacturing processes.
2. Description of Related Art
During the manufacturing of many different types of products, it is often necessary to splice together different sections of a material supply coming from a continuous supply source. Such products include, but are not limited to, sheet insulation, circuit boards, disposable diapers, gaskets, and various types of paper products. Ordinarily, in order to allow the production equipment to run continuously, when any given supply roll of material is exhausted, a new supply roll is spliced in immediately without stopping production. The result is that the machines are constantly running and that some of the finished units of production (e.g., individual disposable diapers) contain a splice where a new roll of material was spliced to an old roll of material. These units of production are considered defective and are not sold to consumers. Therefore, near the end of the production line, there must be a way to locate the splices so that units of production which contain the splices may be rejected.
Currently, splices are located using a timing algorithm which takes into account the initial location of the splice at an initial point in time and the speed of the splice through the production line. Using this information, the arrival time of the splice at a rejection mechanism is estimated, and units of production which are likely to have a splice contained therein are rejected.
The disadvantage of this approach is that there is a large amount of error in predicting the arrival time of the splice at the rejection mechanism. The error arises because the material can stretch and because there can be slippage between the rollers which drive the movement of the material and the material itself. This stretching and slipping causes the splice to travel along the production line at a speed which is different than the assumed average speed of the production line. Therefore, as a result of this error, many additional (e.g., twenty to fifty units of production) are currently rejected for each splice in order to ensure that the one unit of production which actually contains the splice is also rejected. Disadvantageously, therefore, the error in predicting the arrival time of the splice at the rejection mechanism results in a significant amount of waste.